The subject matter disclosed herein relates to hydraulic motion control and, in particular to hydraulic fluid regeneration in a hydraulic motion control system.
Motion of a hydraulic cylinder is the result of the force balance between the load acting on the cylinder, the force of the pressure acting on one side of the cylinder piston and the force of the pressure acting on the other side of the cylinder piston. In typical systems one side of the cylinder is routed to a low-pressure reservoir, as a result the force seen by pressure on that side of the piston is typically negligible. The motion of the cylinder is then a function of the load and the pressure acting on the other side of the cylinder piston; this pressure shall be referred to as the control-pressure. The system controls the rate of cylinder actuation by changing control-pressure to shift the force balance causing the cylinder to decelerate, accelerate, or remain at a steady rate.
Controlling motion of a hydraulic cylinder acting on a load is typically achieved by throttling of the hydraulic fluid through a variable orifice such as a proportional direction control valve. The rate of a hydraulic cylinder output is controlled by changing the size of the control valve orifice to either increase or decrease the pressure drop of the high-pressure fluid coming from the power supply to some lower control-pressure through a throttling process. To increase the cylinder rate, or to react to an increasing load, the orifice would be increased in size, thereby reducing pressure drop through the valve and increasing control-pressure of the fluid flowing to the cylinder. Conversely, to decrease the cylinder velocity, or to react to a decreasing load, the orifice would be decreased in size, thereby increasing pressure drop through the valve and decreasing the control-pressure of the fluid flowing to the cylinder.
Typical hydraulic systems include a hydraulic power source providing flow of high-pressure hydraulic fluid. The high-pressure fluid passes though a control valve where the pressure is reduced to some lower control-pressure and then routed to a hydraulic machine such as a cylinder. The control valve may control which side of a piston head within the cylinder the control-pressure fluid is provided to and, thereby, control motion of the cylinder. The control valve may also route fluid exiting the cylinder to a low-pressure reservoir.
Multiplying the pressure drop through the control valve by the flow rate gives the power dissipated, or lost, by the control valve. The larger the pressure drop the larger the losses. For a system with varying loads on the cylinder this method is very inefficient. If the force on the cylinder becomes such that it aids its motion, the control valve must decrease its orifice size to prevent acceleration of the cylinder. Even with a reduced orifice, fluid from the hydraulic power source is still consumed and its energy dissipated by the control valve. The energy added to the system by the aiding force on the cylinder is also dissipated by the control valve. The dissipated energy causes an increase in the hydraulic fluid temperature.
Some actuation systems utilize a passive regeneration system which allows fluid exiting the rod end of the cylinder to flow back to the hydraulic power source supplementing flow from the hydraulic power source. In order for this type of regeneration to work, the pressure entering the cylinder and the pressure exiting the cylinder must be the same. Actuation force is developed due to the different surface areas on either side of the piston head due to the presence of the single-rod cylinder coupled to one side thereof. However, the actuation force created by such a system is not as large as is possible for a given cylinder not using passive regeneration. Passive regeneration can only be used on single-rod cylinders.